Pituitary function is rarely considered in the care of patients with traumatic brain injury (TBI). Yet,TBI poses significant risk to pituitary function given the gland's encasement within the sella, its delicate infundibular-hypothalamic structures and vulnerable vascular supply. Autopsy studies of fatal head injury victims confirm that up to one third sustain pituitary necrosis and hundreds of case reports document chronic post-traumatic pituitary failure. The long-term neurobehavioral problems that plague a majority of TBI victims are quite similar to those of patients with hypopituitarism. It is the primary hypothesis of this study that many TBI victims suffer from unrecognized pituitary dysfunction that acutely and chronically compounds the initial brain injury and limits maximal recovery. The major hypotheses being tested in this study are that i) post-traumatic pituitary failure, both acute and chronic, results primarily from a vascular insult to the pituitary gland and/or its hypothalamic-infundibular connections; ii) in the acute phase of TBI such injury can result in acute. secondary adrenal insufficiency, iii) in the chronic phase of TBI such injury can result in long-term hypopituitarism, and iv) treatment of pituitary hormone deficiencies will improve neurobehavioral functioning and quality of life in the chronic post-traumatic state. These hypotheses will be tested in a three-phase study. In the first phase, acutely post-injury, subjects will undergo serial determinations of adrenocortical function to diagnose and treat acute adrenal insufficiency. Patients found to have inappropriately low cortisol levels, will be randomized to placebo or hydrocortisone therapy for 48 hours, and changes in blood pressure and vasopressor requirements will be monitored. Pituitary/hypothalamic MRIs will also be performed at 10 days and 6 months post-injury to assess for acute structural lesions and chronic pituitary volumetric changes. In the second phase, at 2 and 6 months post-injury, pituitary function tests will be performed. Hormone deficient patients will be placed on hormone replacement except for growth hormone (GH) after the 2-month time point. In the third phase, from 6 to 12 months post-injury, TBI patients with GH deficiency or GH insufficiency, who have memory impairment, concentration deficits, depression, anxiety or fatigue will be entered into a double-blind placebo-controlled GH replacement therapy trial to assess changes in these neurobehavioral and quality of life complaints. By diagnosing and treating both acute and chronic traumatic neuroendocrine deficiencies, this study may dramatically improvethe long-term prognosis of many TBI patients.